Optical apparatus with spectral filters for testing fastness of colors

ABSTRACT

Apparatus and method for obtaining a detectable variation in a sample in response to radiation. The apparatus includes a source of radiation and a sample to be tested. Filters and a moveable shading device are disposed between the source of radiation and the sample to provide for irradiating different portions of the sample with radiation of the same light intensity per unit time to study the influence of different wavelengths on a sample. The apparatus enables one to determine the minimum wavelength which will bring about a degradation or disintegration of the sample under test.

United States Patent [191- Mar. 19, 1974 Kockott 1 OPTICAL APPARATUSWITH SPECTRAL 3.188.218 6/19 65 Elmer et a1. 240/11 x FILTERS O INGFASTNESS 0 3.426.590 2/1969 Suga 1.818.687 8/1931 Buttolph 73/150 COLORSInventor: Dieter Kockott, Dammstrasse 11.

D6451 Ruckingen. Germany Filed: Oct. 12, 1971 Appl. No.: 188.567

Related US. Application Data Continuation-impart of Ser. No. 5.554. Jan.26. 1970.

US. Cl 350/269, 73/432 SD, 240/l.1, 356/256 Int. Cl. G02f 1/30 Field ofSearch 73/150, 432 SD; 350/266, 350/269, 271, 273, 275, 317; 240/1.1

References Cited UNITED STATES PATENTS 12/1967 Rendina 240/11 X 8/1967Bickler et a1 350/311 UX Primary Examiner-Ronald L. Wibert AssistantExaminer-Paul K. Godwin Apparatus and method for obtaining a detectablevariation in a sample in response to radiation. The apparatus includes asource of radiation and a sample to be tested. Filters and a moveableshading device are disposed between the source of radiation and thesample to provide for irradiating different portions of the sample withradiation of the same light intensity per unit time to study theinfluence of different wavelengths on a sample. The apparatus enablesone to determine the minimum wavelength which will bring about adegradation or disintegration of the sample under test.

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A T TORNEY PATENTEUMAR I 91974 sum 2 0? 2 Fig OPTICAL APPARATUS WITHSPECTRAL FILTERS FOR TESTING FASTNESS OF COLORS CROSS-REFERENCE TORELATED APPLICATION The present application is a continuation-in-partapplication to co-pending US. Pat. application Ser. No. 5,554 filed Jan.26, 1970 now abandoned, entitled Optical Radiation Apparatus forDetermining the Minimum Wavelength."

The present invention relates to an apparatus and a method for obtaininga detectable variation in the sample in response to radiation. in oneparticular embodiment of the invention, there is provided an opticalradiation apparatus to achieve a visible or otherwise detectableradiation degradation or disintegration of materials. such as colorsamples, various paints, varnishes, synthetic plastics and the like, andother materials.

BACKGROUND OF THE INVENTION The purpose of the present invention is toattain a simple measuring method in order to determine the lightfastness of various materials, and to receive quickly quantitativeresults of the light fastness of the tested materials or samples withlittle or no wasting of time. A characteristic parameter for testing thelight fastness of a material or sample is the minimum wavelength whichcauses degradation or disintegration of the material being tested. Thementioned minimum wavelength is defined by the fact that for allwavelengths smaller than, or equal to the minimum wavelength absorptionprocesses take place in the irradiated material or sample which producevisible or otherwise detectable alterations, e.g., decolorations,yellowing, or changes in the mechanical properties of the material orsample under test.

For different degradation or disintegration processes there may existvarious minimum wavelengths. The shorter the minimum wavelength, thegreater is the fastness to light of the material or sample.

There are some apparatus which are already known for testing lightfastness and the capability of resisting weather influences of variousmaterials. The mentioned known apparatus include a centrally locatedlight or radiation source and means to produce extreme weatherconditions.'The light or radiation source simulates, with its sunlikespectrum, the daylight. With the known apparatus, the energy per unittime of irradiation to the sample is considerably greater than thatwhich occurs in daylight, so that the samples undergo quickeralterations than would occur with the radiation with natural daylight.

In addition to the aspired time shortening, there is of interest thequestion of the reason for the material change in theirradiated samplein order to undertake appropriate measures to improve the material beingtested. Each material has the characteristic of manifesting degradationor disintegration to a minimum wavelength.

Certain testing apparatus of a known type, which include a combinationof irradiation apparatus and weather equipment, effect a change in thematerial being tested without answering the question; which wavelengthof the spectrum causes such change? Furthermore, with the known testingapparatus, it is not possible to separate from each other degradationcaused by irradiation-and that caused by the weather equipment.

There are other known testing apparatus which make possible themeasurement of one or more minimum wavelengths of a material. Thesetesting apparatus concern laboratory devices which have great opticalre-' sources and permit a very exact measurement of the minimumwavelength. For industrial ,purposes. the knowledge or determination ofthe minimum wavelength with a high degree of accuracy is not necessary,

so that the great resources of these testing apparatus represent adisadvantage. Up to the present time, the known testing devices for thedetermination of the minimum wavelength with a high degree of accuracyalso possess the disadvantages of requiring high technical resources andconsiderable loss of time, whereby the requirement of time shorteningfor the measurement is not attained.

It is accordingly a primary object of the present invention to provide amethod and an optical radiation apparatus for radiation degradationwhich makes it possible, without any excessive technical resources, todetermine the material constant, viz., the minimum wavelength whichcauses degradation or disintegration, which is determinitative of thelight fastness.

SUMMARY OF THE INVENTION The present invention provides an apparatus forobtaining a detectable variation in a sample in response to radiation.The apparatus includes a source'of radiation and a sample to be tested.The apparatus also in-' cludes a wedge or interference sky filter,including at least one filter element, and a moveable shading meanswhich has different formed slots. The filter and shading means aredisposed between the source of radiation and the sample to be tested forirradiating different portions of the sample with radiation of differentwavelengths. v

The present invention also provides a method for using the novelapparatus for obtaining a detectable variation in a sample in responseto radiation including the following steps. The sample to be tested isdisposed in proximity to a source of radiation. The interference filteror cut-on filters, including at least one filter element, is disposedbetween the source of radiation and the sample to be tested forirradiating the different portions of the sample with radiation ofdifferent wavelengths. A moveable shading means having a plurality ofslots therein is disposed between the interference filter and thesample. Then, the variation in the sample under test is detected inresponse to the radiation with different wavelengths, for example, todetermine the minimum wavelength which brings about the mentionedvariation or degradation in the sample.

According to the present invention, there is also provided an opticalradiation apparatus for the irradiation of the sample along its linearextension with radiation of different wavelengths. I

in certain embodiments of the present invention,

there is provided a radiation apparatus for the fanning application, thementioned cut-on filters aresometimes referred to as wedge filters,stage filters, step filters or spectral band filters. The sample andsample support are provided in a fixed or predetermined positionrelative to the interference sky filter or the cut-on filters.

The invention also provides an optical radiation apparatus includingsamples provided with a raster, wherein the markings of the raster arecoordinated relative to the spectral transmittance of the interferencesky filter, or to the absorption edges or bands of the spectral bandfilters, respectively.

Furthermore, the present invention makes it possible to fan or alter acontinuous spectrum into various wavelengths, whereby it is possible todetermine the minimum wavelength which caused degradation ordiswavelength bands an equal number of quanta per unit time impingesupon the sample. Only then is it possible to compare correctly thedegreeof damage or degradation caused by different wavelengths. There are twopractical ways of making such a comparison. Either the comparison iseffected by calculation, or by the spectral distribution of theradiation sources by the use of intermediate filters. Additionalradiation sources can be used in spectrum ranges of low emission of axenon lamp, for example, a low pressure mercury lamp with a flourescentsubstance. Thus it is possible to meet, at least partially, theabove-mentioned requirement.

By the intermediate positioning of a moveable shading means between theinterference sky filter, or the cut-on filter and the sample to betested, the optical density thereof is varied in a longitudinaldirection in such a manner that the different emission of the radia tionsource in the various spectral bands and the different absorption factorof the interference sky filter or cut-on filter along its axis are suchthat the sample is irradiated at all wavelengths by an equal number ofquanta per unit time.

BRIEF DESCRIPTION OF THE DRAWINGS bodiment of the present inventionutilizing a shading means.

FIG. 3 illustrates the plurality of slots of the shading 1 means.

DETAILED DESCRIPTION OF SOME PREFERRED EMBODIMENTS OF THE INVENTION Withreference to FIG. 1, there is shown a radiation source, such as a xenonlamp, which emits a continuous spectrum. The radiation source 12 isarranged in a sample chamber of a radiation apparatus for determin-.

ing the minimum wavelength. The radiation source 12 is supplied withelectric currents through conductors or connections 14. Asemi-cylindrical, parabolic or eliptical mirror 22 which is disposedabove the radiation source 12 reflects the upward irradiated light ofthe radiation source 12 towards a sample 18. Thus, the irradiationstrength applied to sample 18 is increased.

In a first embodiment of the invention, a wedge or interference skyfilter 16 is arranged at a predetermined distance a from the radiationsource 12 and disposed between the radiation source and the sample 18.The sample 18 to be tested consists, for example, of colors, paints.varnishes, synthetic plastic coatings, etc., and is placed on a samplesupport 20.

Before being irradiated, the sample 18 is provided with a stable orfixed raster for the purpose of marking the various wavelengths. Thesample 18 and the sample support 20 are provided in a predetermined orstationary position relative to the interference sky filter 16, wherebythe sample 18 abuts or lies against the interference sky filter 16. Inpractice, the apparatus maybe constructed in such a form as to besuperimposed upon the material and thereby provide for testing ofgreater or extensive surfaces.

Referring again to FIG. 1, the sample support 20 rests upon a basesupport 24 which is swingable out of the sample chamber 10 to provide aquick and easy exchange of the samples 18. Prior to irradiation, theras' ter is placed in a length direction upon the sample 18 in such away that the marks or lines of the raster are coordinated with thespectral transmittance of the interference sky filter 16.

If desired, a heat absorption filter 28 may be disposed between theradiation source 12 and the interference sky filter l6 and arranged toprevent an excessive heating of the sample 18. Also, if desired, theradiation apparatus may include a mechanism (not shown) for theautomatic control of the humidity of the air and for the weathering ofthe sample 18 in the sample chamber 10. This mechanism may be providedas an additional equipment for samples whose degradation is sensitive tohumidity, for example, varnishes. 7

There may be employed several wedge filter, cut-on or spectral bandfilters 26 which are marked out by a steep absorption edge instead ofthe interference sky filter 16, the spectral transmittance of whichchanges continuously over a length direction of the filter. The cut-onfilter has a predetermined level of radiation absorption above which itwill pass radiation having a wavelength greater than the predeterminedlevel. Thus, below a wavelength M, which is coordinated to the edge ofthe cut-on filter, all the radiation is absorbed; and for A A thetransmittance is extremely high.

If, subsequent to irradiation, under a certain cut-on filter 26 secondfilter having a a a change of the sam ple occurs, but which was notobserved or noted in the case of a certainfirst filter A, then theminimum wavelength must be between the two X, of the mentioned filtersi.e., A, and A In the case of a sufficiently dense sequence of the A),it is possible to achieve a satisfactory precision in determining theminimum wavelength. The primary advantage offered by this processresides in the shorter testing time. Whereas in the case of theinterference sky filter 16 only a very small wavelength band of theradiation impinges upon each point of the sample, and thus only afractional portion is exposed to the radiation of the source. Whereas inthe case of the cuton or spectral band filters, an integration isachieved over all wavelengths k t and consequently a greater irradiationstrength is applied to the sample.

' ation source 12 is arranged in a sample chamber of the radiationapparatus for determining a minimum wavelength. The radiation source 12is supplied with electric currents through conductors or connectors 14.

A semi-cylindrical, parabolic or eliptical mirror 22 which is disposedabove the radiation source 12 reflects the upward irradiated light ofthe radiation source 12 towards a sample 18.

In both the embodiments of FIG. 1 and FIG. 2, a sky interference skyfilter 16 is arranged at a predeter support are provided in apredetermined or stationary position relative to the interference skyfilter 16, whereby the sample 18 is spaced apart of the interference skyfilter 16. The moveable shading means 3 having the plurality of spacedapart slots 5 disposed therein is placed between the interference skyfilter l6 and the sample 18.

In practice, the apparatus may be constructed in such a manner as to besuperimposed on the material and thereby provides for testing of greateror extensive surfaces.

Referring to FIG. 2, the smaple support 20 rests upon the base support24 which is swingable out of the sample chamber 10 to provide a quickand easy exchange of the samples 18. Prior to radiation, the raster isplaced in a lengthwise direction upon the sample 18 in such a way thatthe marks or lines of the raster are coordinated with the spectraltransmittance of the interference sky filter 16. The moveable shadingmeans 3 may be driven by a motor 17 at a speed of l to 2 cycles persecond past the sample 18.

If desired, a heat absorption filter 28 may be disposed between theradiation source 12 and the interference filter 16 and arranged toprevent an excessive heating of the sample 18. Also, if desire, theradiation apparatus may include a mechanism (not shown) for theautomatic control of the humidity of the air or for the weathering ofthe sample 18 in the sample chamber 10. This mechanism may be providedas an additional piece of equipment when testing samples whosedegradation is sensitive to humidity, for example, varnishes.

As with the first embodiment illustrated in FIG. 1, the embodiment ofFIG. 2 may employ several cut-on or spectral band filters 26 which aremarked out by a step absorption edge instead of the interference skyfilter 16, the spectral transmittance of which changes continuously overa length in the direction of the filter.

In another embodiment which utilizes a wedge filter 26 in place of theinterference sky filter l6, radiation from source 12 impinges on acertain first wedge or cut-on filter 26. This filter passes only awavelength A The radiation A, then impinges on the moveable shadingmeans 3 which is translating passed the sample 18 at from I to 2 cyclesper second. The plurality of slots 5 intermittently allow the radiationto pass through to impinge upon the sample 18. The slots 5 in theshading means 3 thereby assure that every point along the sample 18receives a uniform radiation intensity per unit time impinging along thelinear exterior of the entire sample to obtain a uniform degree ofexposure of the entire sample. v

Subsequently, the sample 18 is tested utilizing a certain second wedgeor cut-on filter 26 which passes only a wavelength A,.

If a change of the sample occurs when testing using the second wedgefilter 26, but no change in the sample was observed or noted when thesample was tested using the first wedge filter 26, then the minimumwavelength which causes disintegration or degradation ust lie betweenthe minimum wavelengths passed by the respective filters, i.e., A, and AThe advantage offered by this process and apparatus resides in a shortertesting time, and also in the fact that the entire sample is exposed tothe same light intensity per unit time which results in comparableconditions on the sample 18 making it possible to study the influence ofdifferent wavelengths on the sample being tested. If the shading means 3is not used, both factors involving sample degradation ordisintegration, namely, different wavelengths and different intensitiesper unit time are superimposed and not separable making it impossible todetermine if the effect at comparable points on the sample is the resultof only a wavelength of the radiation or the result of differentlight-intensities.

The width, spacing, and form of the slots 5 in the shading means 3 is afunction of the wavelengths of the radiation source used and isdetermined experimentally.

I claim: I

1. An apparatus for obtaining a visible or otherwise detectablevariation or radiation degradation in a sample in response to radiation,comprising, in combination:

a source of radiation disposed within said apparatus; said sample to betested is disposed within said apparatus stationary relative to saidsource of radiation; a wedge filter disposed between said source ofradiation and said sample to be tested, said wedge filter I having apredetermined level of radiation absorption above which it'will passradiation having a wavelength greater than the predetermined level;

a moveable shade means having spaced apart slots therein, said shademeans being disposed between said wedge filter and said sample;

a motor operatively associated with said moveable shade means to driveit past said sample to produce a uniform radiation intensity per unittime impinging along the linear exterior of said sample; and

wherein said sample is irradiated with radiation passed by said wedgefilter.

2. An apparatus as defined in claim 1, wherein a ,heat absorption filteris disposed between said source of radiation and said movable shademeans.

3. An apparatus for obtaining a visible or otherwise detectablevariation or radiation degradation, comprising in combination; i

a source of radiation disposed within said apparatus;

a sample to be tested disposed within said apparatus and beingstationary relative to said source of radiation;

an interference sky filter disposed between said source of radiation andsaid sample to be tested to 7 8 separate said radiation into itscomponent waveto produce a uniform radiation intensity per unit lengths;time impinging along the linear extension of said a raster disposed oversaid sample to be tested having sample; and v markings, which arecoordinated with the spectral wherein said sample is irradiated withradiation sepatransmittance of said sky filter; rated into its componentwavelengths passed by a moveable shade means having spaced apart slotssaid interference sky filter. I

therein, said shade means being disposed between 4. An apparatus asdefined in claim 3, wherein said said interference sky filter and saidsample; motor drives said movable shade means past said sama motoroperatively associated with said moveable ple at a speed of from 1 to 2cycles per second.

shade means to drive it cyclically past said sample 10 v

1. An apparatus for obtaining a visible or otherwise detectablevariation or radiation degradation in a sample in response to radiation,comprising, in combination: a source of radiation disposed within saidapparatus; said sample to be tested is disposed within said apparatusstationary relative to said source of radiation; a wedge filter disposedbetween said source of radiation and said sample to be tested, saidwedge filter having a predetermined level of radiation absorption abovewhich it will pass radiation having a wavelength greater than thepredetermined level; a moveable shade means having spaced apart slotstherein, said shade means being disposed between said wedge filter andsaid sample; a motor operatively associated with said moveable shademeans to drive it past said sample to produce a uniform radiationintensity per unit time impinging along the linear exterior of saidsample; and wherein said sample is irradiated with radiation passed bysaid wedge filter.
 2. An apparatus as defined in claim 1, wherein a heatabsorption filter is disposed between said source of radiation and saidmovable shade means.
 3. An apparatus for obtaining a visible orotherwise detectable variation or radiation degradation, comprising incombination; a source of radiation disposed within said apparatus; asample to be tested disposed within said apparatus and being stationaryrelative to said source of radiation; an interference sky filterdisposed between said source of radiation and said sample to be testedto separate said radiation into its component wavelengths; a rasterdisposed over said sample to be tested having markings which arecoordinated with the spectral transmittance of said sky filter; amoveable shade means having spaced apart slots therein, said shade meansbeing disposed between said interference sky filter and said sample; amotor operatively associated with said moveable shade means to drive itcyclically past said sample to produce a uniform radiation intensity perunit time impinging along the linear extension of said sample; andwherein said sample is irradiated with radiation separated into itscomponent wavelengths passed by said interference sky filter.
 4. Anapparatus as defined in claim 3, wherein said motor drives said movableshade means past said sample at a speed of from 1 to 2 cycles persecond.